A prior art articulated manipulator proposed in Patent document 1 has an angular joint connecting two arm members. The angular joint connects two arm members such that one of the two arm members is able to precess relative to the other arm member. The arm member which precesses turns about an axis of rotation inclined at a predetermined angle to the axis of the arm member. The articulated manipulator provided with the angular joint moves an object held on its free end to a desired position.
Another prior art articulated manipulator proposed in Patent document 2 or 3 is provided with arm members successively connected in a linear arrangement and forming a hollow space extending therethrough. Power cables and signal cables are extended in the hollow space to form power transmission lines for transmitting power for driving the arm members for rotation and signal transmission lines in the articulated manipulator.
Patent document 1: JP 62-148182 A
Patent document 2: JP 10-225881 A
Patent document 3: JP 2001-138279 A
The articulated manipulator disclosed in Patent document 2 has a hollow space for holding wires therein. The articulated manipulator is provided with a coreless direct electric motor, namely, the so-called hollow direct motor, to form the hollow space. Linear members, such as power lines and signal lines, are passed through the hollow direct motor and are extended along the respectively axes of the arm members.
The hollow direct motor has a stator fastened to one of two arm members, and a rotor fastened to the other arm member. The hollow direct motor is a motor having a special shape, namely, an annular shape. Therefore, the manufacturing cost of the articulated manipulator provided with the hollow direct motor is high. This articulated manipulator has problems; hollow direct motor has a small power capacity for its size, an encoder cannot be disposed on the axis of rotation, and accurate positioning cannot be achieved.
The articulated manipulator disclosed in Patent document 3 has arm members individually provided with built-in motors, respectively. Since each arm member is provided with the built-in motor, the arm member cannot be miniaturized in a size smaller than that of the built-in motor and, consequently, the articulated manipulator cannot be sufficiently miniaturized. The driving force of the motor is transmitted by an internal bevel gear or a belt.
The internal bevel gear is formed by complicated machining. Since an input shaft in the center of the motor and the output shaft of a reduction gear do not intersect perpendicularly each other, support members need accurate machining and accurate assembling. Since hollows in the bevel gear and the reduction gear are not sealed, lubricant, such as grease or oil, leaks. The motor disposed inside the bevel gear affects adversely to the efficiency of utilization of the hollow.
When the belt is employed, a tension adjusting mechanism is needed, the arm member must be designed so as to hold the belt and, consequently, the construction of the arm member is inevitably complicated.